To make both compatible in reducing a cooling loss caused due to a temperature difference between combustion gas and a cylinder wall surface, and improving emission, in an engine 1 which injects fuel into a combustion chamber 17 by an injector 33 and combusts it.

Preceding injection for injecting fuel by an injector 33 in a compression stroke and succeeding injection for injecting the fuel by the injector 33 in an expansion stroke, are performed so as to finish combustion before injection fuel supplied into a combustion chamber 17 by the respective injections reaches a cylinder wall surface, so that an air heat insulation layer 50 is formed between the combustion gas and the cylinder wall surface in preceding combustion and succeeding combustion.